The present invention concerns a process and an apparatus for the reclaiming of desirable materials from rubber waste, in particular scrap tires.
Approximately 3.2 million tons of scrap tires arise per year in the European Union. In the past most scrap tires were deposited in landfills. Since the year 2003 an EU Guideline has prohibited the dumping of scrap tires. Currently, scrap tires are burnt as boiler fuel in particular in the cement industry. Other used vehicle tires are recycled to be used in pavements.
Pyrolysis of scrap tires has also been known for many years. By pyrolysis which is carried out in the absence of oxygen at above 500° C. and which is an endothermic process the scrap tires are decomposed. Thus, substantial amounts of carbon black, steel, oil and gas can be recovered from the scrap tires. However, the pyrolysis processes for scrap has failed to become widely established in particular due to the low quality of the pyrolysis products which do not satisfy the commercial requirements.
In EP 1 163 092 B1 a pyrolysis process for scrap tires is disclosed in which a pyrolysis chamber with three heating zones comprising different temperatures is provided. The scrap tires are fed as granulate to the pyrolysis chamber comprising different heating zones. The pyrolysis chamber is rotated with respect to the flight to transport the granulated tire pieces. A first heating zone of the pyrolysis chamber has a temperature between 700° to 800° C. A second heating zone of the pyrolysis chamber has a second temperature between 600° to 700° C. A third heating zone has a temperature between 500° to 600° C.
In U.S. Pat. No. 6,835,861 B2 a low energy method of pyrolysis of rubber material is disclosed. The rubber material is inserted together with a clay catalyst into an pyrolysis apparatus with three different heating phases in a first embodiment. In the first phase, called activation phase, the rubber material is heated to temperature between 68.3° to 287.8° C. In the second phase the reaction temperature is held between 287.8° C. and 454.4° C. In the third phase the temperature is held at the same level by heating. In a second embodiment, which is also disclosed in U.S. Pat. No. 6,833,485 B2 and U.S. Pat. No. 7,341,646 B2 the rubber material is transported through three different zones, each zone comprising a temperature of preferably about 287.8° C. In both processes the catalyst is not removed after conclusion of the pyrolysis.
As mentioned above, one problem in the known processes for scrap tires is that the quality of the carbon black recovered is outside the commercial specifications for carbon black due to the either too high or too low temperature of the processes. Therefore the recovered carbon black is of only limited commercial use.
Consequently, it is one object of the present invention to provide a thermal treatment process and an apparatus for thermal treatment of rubber waste, in particular scrap tires, which provide recovered material of such high purity that it can be commercially used.